Telephone system



Sept. 17, 1940. c. E. oMAx Er Ax.

TELEPHONE SYSTEM Filed April 21. 19259 5 Sheets-Sheet l I7 JNHUIQI @meNSG S l :SQ

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Timm Sept. 17, 1940. c. E, LoMAx ET AL TELEPHONE SYSTEM Filed April 21,1939 5 Sheets-Sheet 2 ON Oem BY PIER BAKKER ATTORNEYS.

INVENToRs ATTORNEYS.

25l Sheets-Shee't 3 Sept. 17, 1940- c. E, LoMAx Er AL TELEPHONE SYSTEMFiled April 21, 1939 CLARENCE E. LOMAX BY I P/EP BAKKER MIM,MV0MJPatented Sept. 17,

i TELEPHONE SYSTEM Clarence E. Lomax, Oak Park, and Pier Bakker?-Chicago, Ill., assignors to Associated Electric Laboratories, Inc.,Chicago, lll., a corporation of Delaware Application April 21, 1939,Serial No. 269,139

10 Claims.

The present invention relates to telephone systems and, moreparticularly, to automatic telephone systems in which nder switches areemployed to extend connections between calling lines and selectorswitches. f

It is an object of the present invention to provide, in an automatictelephone system, improved distributor apparatus for selecting idlefinder switches for the use of calling lines and for lclantrolling theoperations of the selected finder switches.

Another object of the invention is to provide, in an automatic telephonesystem of the character noted, improved apparatus for testing theoperations of the distributor apparatus and the finder switches, whichtesting apparatus is so connected and arranged that it does notinterfere with the handling of tratlic in the system.

A further object of the system is to provide, in an automatic telephonesystem of the character noted, an automatic switch embodying improvedtesting apparatus for controlling the operation thereof, which testingapparatus is connected and arranged to prevent false operation of theswitch when it engages a busy line having a metering potential connectedto the control conductor thereof.

The features of the present invention are illustrated as beingincorporated in a telephone system provided with an exchange terminatingfirst and second groups of lines and comprising rst and second groups offinder-selector links, each link including a finder switch and aselector switch, rst and second groups ofl connector switches, and firstand second distributors respectively associated with the rst and secondgroups of links. These switches are so connected and arranged that eachfinder switch has access to each line of the system; each selectorswitch has access to each connector switch; and the connector switchesin the rst and second groups of connector switches respectively haveaccess to the lines in the first and second groups of lines.

In accordance with one feature of the invention, each of the finderswitches includes rst and second' wiper sets movable in vertical androtary4 directions and respectively having access to the first andsecond groups of lines, vertical and rotary magnets operative'respectively to control the vertical and the rotary movements of thewiper sets, a trunk line normally disconnected from the wiper sets,first and second switching relays operative respectively to connect therst and. Sond wiper sets to the trunk line, and means responsive to theoperation of one of the switching relays for preventing the operation ofthe other of the switching relays. The distributor associated with eachgroup of nder switches comprises a rotary switch operative to select anidle one of the nder switches in the group, means for governing therotary and the vertical magnets of the selected nder switch, a firsttest relay operative in response to the seizure of a calling line by thefirst wiper set in the selected nder switch, a second test relayoperative in response to the seizure of a calling line .by the secondwiper set in the selected finder switch, means responsive to theoperation of the rst test relay for causing the operation of the firstswitching relay in the selected finder switch, means responsive to theoperation of the second test relay for causing the operation of thesecond switching relay in the selected finder switch, and meansresponsive to the operation of either one of the switching relays in theselected finder switch for causing the operation of the rotary switch.

More particularly, the rst and second test relays in the distributor areindividually provided with operating circuits, each operating circuitincluding a uni-directional current conducting device in the form of acopper oxide rectifier. The arrangement of the copper oxide rectifier inthe operating circuits of the first and second test relays preventsthese relays from being energized when these operating circuits arecompleted in such a manner that current tends to flow therein in adirection opposite to that of the normal flow of current therein. Thisarrangement prevents false operation of the first and second test relayswhen the rst and second` wiper sets in the selected finder switchrespec-a tively engage busy lines having a metering potential connectedto the control conductors 40 thereof.

In accordance with another feature of the invention, each of thedistributors includes a transfer relay provided with an operatingcircuit; and means is included in each idle nder switch in theassociated group of nder switches for completing the operating circuitof the transfer relay, whereby the voperating circuit of the transferrelay is interrupted when all of the finder switches in the associatedgroup are busy. First and second start conductors are provided which areoperatively associated with the rst 'and second groups of lines, wherebystart potentials are connected to the start conductors in re- Spouse t9the creatien 0i calling conditions 0n Cil - restored position.

lines in the respective groups oi' lines. The first start conductor isassociated with the first distributor, when the transfer relay in thefirst distributor occupies its operated position, and is associated withthe second distributor, when the transfer relay in the first distributoroccupies its The transfer relay in the second distributor controls theassociation of the second start conductor with the first and seconddistributors in a similar manner. Operation of each of the distributorsis initiated when a start potential is connected to a start conductorassociated therewith; and each of vthe distributors is effective whenoperation thereof is initiated to cause a selected one of the finderswitches in the associated group to find a line having a callingcondition thereon. Also, each of the distributors includes timing meansoperative to interrupt the operating circuit of the transfer relaytherein in the event the finder switch selected thereby fails tooperate. In order to test the operations of the distributors and thefinder switches associated therewith, manually operable means comprisinga busy switch and a number of test jacks is individually associated witheach of the distributors.

In accordance with another feature of the invention, the selector switchof each of the links comprises a test relay having a field structureprovided with a first magnetic path including a shunt leg and a secondmagnetic path including a movable armature, first and second windingsbeing associated with the field structure. A first circuit is providedfor energizing the first winding; and a s econd circuit'includingatest'wiper of the finder switch is provided for energizing the secondwinding. The first winding is effective, when energized with currentflowing in the first circuit, to produce a magnetic flux in the fieldstructure traversing the first magnetic path; the second winding iseffective, when energized with current flowing in a first direction inthe second circuit, to produce a magnetic flux in the field structuretraversing the first magnetic path; and when energized with currentflowing in a second direction in the second circuit to produce amagnetic flux in the field structure opposing the magnetic fluxtraversing the shunt leg, thereby to 'divert magnetic flux from thefirst magnetic path into the second magnetic path. The test relay is soconstructed and arranged that it is operated when magnetic fluxtraverses the second magnetic path. The selector switch comprisesautomatic means operative to drive the test wiper thereof step by stepover a group of test contacts in the contact bank thereof; lwhich testcontacts are adapted to have connected thereto an idle potential, a busypotential, or a metering potential, depending upon the condition of theassociated line. The second circuit is so connected and arrangedthat nocurrent flows therein, when the test wiper engages a test contact havinga busy potential connected thereto; that current flows therein in thefirst direction, when the test wiper engages a test contact having ametering potential connected thereto; and that current flows therein inthe second direction, when the test wiper engages a test contact havingan idle potential connected thereto. Further, each selector switchcomprises means controlled by the operation of the test relay thereinfor arresting the operation of the automatic means.

Further features of the invention pertainto the particularl arrangementof the circuit elements of the system and to the particular connectionand arrangement of the elements of the distributors and the linksincorporated therein, whereby the above-outlined and additional featuresare attained.

The novel features believed to be characteristic of the invention areset forth with particularity in the appended claims. The invention, bothas to its organization and method of operation, together with furtherobjects and advantages thereof, will best be understood by reference tothe following specification taken in connection with the accompanyingdrawings in which Figures 1 to 3, inclusive, illustrate a telephonesystem embodying the present invention.

Referring now more particularly to Figs. 1 to 3, inclusive, of thedrawings, the telephone system there illustrated comprises an exchangeincluding an operator position 2I0 and terminating a plurality ofsubscriber lines, including the subscriber lines IUI and 230. Also, theexchange comprises a number of links, including the links 60 and 10, anda number of connector switches including the connector switch 2|5 forsetting up connections between the various lines. More specifically, theexchange `has an ultimate capacity of 200 lines, these lines beingarranged in first and second groups of lines each. Each of the linkscomprises a 200 point finder switch having access to each line in thesystem and a 100 point selector switch having access to each of theconnector switches; while the connector switches are of the 100 pointtype and are arranged in first and second groups, respectively, Vhavingaccess to the first and second groups of lines of the system.

Furthermore, the links are arranged in first and second groups, eachgroup of links being provided with a distributor individual thereto forassigning idle ones of the links in the group to the use of calling onesof the lines. The number of links included in each group is determinedby the amount of traiiic which the exchange is required to handle andusually satisfactory service may be rendered when each of the two groupsof links includes ten links. Also, the number of connector switchesrequired is determined by the amount of traffic which the exchange isrequired to handle and usually satisfactory service may be rendered wheneach of the two groups of connector switches includes ten connectorswitches.

More particularly, the first group of links includes the link 60, whichcomprises the finder `switch |30 and the selector switch 200, and isprovided with the distributor 300; while the second group of linksincludes the link 10, which comprises the nder switch 3|!) and theselector switch 3| I, and is provid-ed with the distributor 3| 2. Thefirst and second groups of lines are respectively associated with thedistributors 300 and 3|2; whereby calling lines in the first group oflines are normally assigned for use idle ones of the links in the firstgroup of links, and calling lines in the second group of lines arenormally assigned for use idle ones of the links in the second group oflinks, thereby rendering it possible to extend simultaneously a callinitiated on a line in each of' the two groups of lines. Furthermore,the distributors 300 and 3|2 are so connected and arranged that a. callinitiated on a line in the first group of lines is assigned for use anidle link in the second group of links in the event all of the links inthe first group of links are busy; and a call initiated on a line in thesecond group of lines `is assigned for use an idle link in the firstgroup of links in the event all of the links in the second group oflinks are busy.

A subscriber substation is associated with each of the subscriber lines,the subscriber substations A and B being respectively associated withthe subscriber lines and 230. Each of the subscriber substations isprovided with a telephone instrument, a dial mechanism and a ringer.Also, a line circuit is individually associated with each of thesubscriber lines, the line circuits |00 and 240 respectively illustratedin Figs. 1 and 2 being respectively associated with the subscriber lines|0| and 230. Preferably, these line circuits are identical, eachincluding a line relay and a cutol relay, these relays in the linecircuit |00 being respectively' indicated at R|20 and R||0, and theserelays in the line circuit 240 being respectively indicated at R2 50 andR245. Furthermore, a meter relay is associated with each of the linecircuits, these relays associated with the line circuits |00 and 240being respectively indicated at Rl09 and at R2l9.

Preferably, each of the links is connected and arranged in a mannersimilar to that of the link 60 which comprises the finder switch |30 andthe selector switch 200. The finder switch |30, as best shown in Fig. 1,comprises a switching mechanism |40 of-the Strowger type including abank of fixed contact sets arranged in ten vertical levels, each levelincluding upper and lower rows of contact sets, each row of contact setsincluding ten radially disposed contact sets, each contact setterminating a line extending thereto; and a row of fixed contactsarranged in vertical alignment. Also, the Strowger mechanismv |40comprises upper and lower wiper sets respectively including the wipers|4I, |42, |43`and |44, |45, |46 carried by a carriage movable in bothvertical and rotary directions, the upper and lower wiper sets beingrespectively associated with the upper and lower rows of contact sets inthe bank of xed contact sets; and a control wiper |41 carried by thecarriage, the control wiper |41 being associated with the row of xedcontacts. Also, this Strowger mechanism includes a vertical magnet M|,10for moving the carriage in the vertical direction, a rotary magnet M|1|for moving the carriage in a rotary direction, and a release magnet M|12for releasing the carriage and for causing it to be returned to itsnormal position. Associated with this Strowger mechanism are two sets ofswitch springs SI15 and SI1!) which are actuated by the movement of thecarriage in the vertical direction away from its normal position, and aset of switch springs S|14 which is actuated by the movement of thecarriage into its eleventh rotary position. Also, it is noted that theupper and lower wiper sets respectively terminate the trunk lines |3|and |35 included in the finder switch |30, which trunk lines areoperatively associated with the trunk line ||5 extending between thefinder switch |30 and the selector switch 200. Also, the

finder switch |30 comprises a start relay R|40, two switching relaysR|50 and R|60, a supervisory lamp L|28 and a manually operable busyswitch SI 83.

The selector switch 200, as best shown in Fig. 2, comprises a switchingmechanism of the Strowger type including a bank of xed contact setsarranged in ten vertical levels, each level including tencircumferentially disposed contact sets, each contact set terminating aline extending thereto. Also, the Strowger mechanism 20| comprises awiper set including the wipers 202,

203 and 204 carried by a carriage movable in both vertical and rotarydirections, the wiper set being associated with the bank of fixedcontact sets. Also, this Strowger mechanism includes a vertical magnetM236 for moving the carriage in the vertical direction, a rotary magnetM231 for a line relay R260, a hold relay R210, a transfer l relay R290,a test relay R265 and a switching relay R2|0.

Preferably, each of the distributors is connected and arranged in amanner similar to that of the distributor 300 individually associatedwith the first group of links which comprises, as best shown in Fig. 3,a rotary switch 30| including six banks of xed contacts and six wipersindividu# ally associated therewith, the corresponding contacts in eachbank terminating the control conductors extending to the respectivelinks in the rst group of links, and the wipers terminating the controlconductors extending to the distributor. Also, the rotary switch 30|includes a rotary magnet M308 for driving the wipers associated with thecontact banks in a rotary direction. The distributor 300 also comprisesa start relay R345, a busy transfer relay R340, a `step relay R310, atransfer relay R360, a timing relay R315, rst and second test relaysR320 and R325, respectively, and a number of control relays R350, R380,R390 and R330. Also associated with the distributor 300 are asupervisory lamp L309, a number of jacks J33I, J332 and .1333 and a busyswitch S334 which are utilized for test purposes in a manner more fullydescribed subsequently.

The distributor 300 is of the preselective type in that an idle link inthe rst group of links is selected to be assigned to the use of acalling line in the first group of lines prior to the initiation of acall on the line therein and another idle link in the first group oflinks is automatically selected to be assigned to the use of the nextcalling line in the first group of lines as soon as the selected linkoperates to find a calling line in the first group of lines. Also, thedistributor 300 is so connected and arranged that, when all of the linksin the rst group of links are busy, the start circuit of the distributor300 is transferred to the distributor 3|2 associated with the secondgroup of lines, whereby the distributor 3| 2 assigns idle ones of thelinks in the second group of links to the use of calling lines in therst group of lines.

Preferably, each of the connector switches is connected and arranged ina manner similar to that of the connector switch 2| 5, which connectorswitch is of conventional connection and arrangement and includes aStrowger mechanism 225 anda battery reversing relay R220. It is notedthat a trunk line 2|| including a control conductor C2|4 extends to theconnector switch 2|5 and that a battery 223 is included in the connectorswitch 2|5 and operatively associated by way of a switching arrangementwith the control conductor C2|4 of the trunk line 2| whereby boosterbattery potential may be applied to the control conductor C2|4 of thetrunk line 2II for metering purposes in a manner more fully describedhereinafter.

Preferably, the operator position 2IU is of conventional connection andarrangement and includes apparatus thereat for answering an incomingcall extending thereto.

A better understanding of the connection and arrangement of theapparatus incorporated in the telephone system will be facilitated froma consideration of the operation thereof incident to the extension of acall from the subscriber substation A to the subscriber substation B.The call is first initiated at the substation A by removing the receiverof the telephone instrument thereat from its hook, thereby to complete abridge path at the substation A between the line conductors CIU2 andC|U3 of the subscriber line IUI extending to the substation A, When'this bridge path is completed between the line conductors of .thesubscriber line' IUI, a circuit is completed for energizing the linerelay RI2U -in the line circuitgIUU individually associated with thesubscriber line IUI, which circuit extends from ground, at RAI I2, byWay of RAI |2, CIU2, the bridge path between the line conductors C|U2and CI03 of the subscriber line IUI, C103, RAI I I, and the winding ofRI to battery. When energized over the above-traced circuit the linerelay R|2U operates to complete, at RAI22 and RC |23, an obvious pathfor applying ground potential to the control conductor C|U5 of thesubscriber line IUI, thereby to mark the subscriber line I'UI as busy tothe connector switches having access thereto. Also, the line relay RI'20completes, at RAl25, an obvious path for applyingground potential to thecontrol conductor CIUU, thereby to cause ground potential to be appliedby way of the circuit network IUI to the start conductor C3I6 extendinginto the distributor 300, assuming that the subscriber line IUI isincluded in the first group of subscriber lines. Also, this applicationof ground potential to the control conductor CI90 marks, by way of thecircuit network |9| and the contacts in the rows of contacts in theStrowger mechanisms included in the nder switches, the levels whereinthe subscriber line IUI is terminated, the contact in the row ofcontacts in the Strowger mechanism |40 included in the finder switch |30being indicated at |48. Also, upon operating, the line relay R|20completes, at RAI2I, a path for applying battery potential to thecontrol conductor CI04 of the subscriber line IUI, thereby to mark therotary positions of the contact sets in the contact banks of theStrowger mechanisms included in the tinder switches terminating thesubscriber line IUI. This path for applying battery potential to thecontrol conductor CIU4 of the subscriber line IUI extends from batteryat the winding of the cutoff relay RII U, by way of the winding of RI IUandRA|2|,toC|U4.

This application of ground potential to the start conductor C3I6extending into the distributor 300 completes a circuit for energizingthe start relay R345, this circuit extending from ground, at RAI 25, byway of the control conductor CI'3I, a resistor included in the circuitnetwork ISI, the start conductor C3IU, RA34I, RC343 and the winding ofR345 to battery. When energized over the above-traced circuit, the startrelay R345 operates to initiate operation of the distributor 300.thereby to cause the preselected idle one of the links in the firstgroup of links to be assigned to the use of the calling subscriber line.Moreparticularly, upon operating, the start relay R345 completes, atRA343, a circuit for energizing the control relay.R350 in series withthe winding of the rotary magnet M303 of the rotary switch 30|, thiscircuit extending from ground, at RA330, by way of RA33U. RC33I, RA335.RA343, the winding of R350, RA345, MA3U3, and the winding of M303 tobattery. When the above-traced series circuit is completed, the rotarymagnet M303 does not operate due to the high series resistance of thewinding of the relay R350. However, the control relay R35U does operate.Upon operating, the control relay R350 completes. at RA353, analternative holding circuit for energizing the busy transfer relay R340,this circuit extending from ground, at RA344, by way of RA344. RAI"V andthe winding of R340 to battery. It is noted that the busy transfer relayR340 is normally energized by way of a number of multiple circuitscompleted in idle ones of the finder switches of 'the first group oflinks, one ofA these multiple circuits being completed at this time inthe finder switch |30 of the link 5U and extending from ground, atRAI44, by way of RAI44, RCI45, the switch springs |85 and |31 of thebusy switch SIU3, the switch springs |13 and |11 of the set of switchsprings SI15, the'all-trunks-busy conductor C32I, the switch springs 335and 330 of the busy switch S334, RA 333, and the winding of R340 tobattery. Also, it will be understood that a similar multiple circuitwill be completed in each of the finder switches of idle ones of linksin the first group of links.

Also, upon operating, the relay R350 completes, at RA355, a point in acircuit traced hereinafter for energizing the timing relay R315,prepares,

at RA351, a point in a circuit traced hereinafter for energizing thelower winding of the transfer relay R300, prepares, at RA353, a point inan alternative circuit traced hereinafter for energizing the windingthereof in series with the winding of the rotary magnet M300 of therotary switch 30|, prepares, at RA353 and RC355, a point in a circuittraced hereinafter for energizing the winding of the rotary magnet M303directly from the guard conductor C322, and prepares, at RA352, a pointin a circuit traced hereinafter for energizing the vertical magnet M|1Uof the finder switch |30 of the link 5U, assuming that the link 5U hasbeen preselected by the distributor 300. Also, the control relay R350completes, at RAI, a circuit traced hereinafter for energizing the startrelay RI of the finder switch |30 of the preselected link 3U. Aspreviously noted, the link 5U in the rst group of links has beenpreviously selected by the distributor 300 ,for the use of a callingline in the first group of lines. Accordingly, the wipers 302 to 301,inclusive, of the rotary switch 30| engage the contacts in theassociated contact banks terminating the control conductors extending tothe finder switch |30.

The circuit for energizing the start relay RI40 in the finder switch |30extends from ground, at RA35I, by way of RA35I, the wiper 303 andassociated contact of the rotary switch 30|, the ilnder start conductorC3I3, and the winding of RI40 to battery. When energized over theabovetraced circuit, the start relay RI40 operates to complete,l atRAI4I, an obvious path between the line conductors CI I6 and CI I1 ofthe trunk line II5 extending between the ilnder switch |30 and theselector switch 200 of the link UU, and to complete, at RA|44 and RCI,an obvious path for applying ground potential to the control conductorCIIB of the trunk line IIS. When the path is completed between the lineconductors CI I6 and C| I1 of the trunk line H5, a circuit is completedfor energizing in series the upper and lower windings of the line relayR260 in the selector switch 200, this circuit extending from ground byway of the upper winding of R260, RC2| 6, RA2I4, CII1, the resistor |21,RAI4I, CII6, RA2I I, RC2|3, and the lower winding of R260 to battery.When energized over the above-traced circuit, the line relay R260operates to interrupt, at RA26I and RC263, a point in a circuit, tracedhereinafter, for energizing the winding of the release magnet M238, andto complete, at RA26I and RC262, a circuit for energizing the hold re-ylay R210, the last-mentioned circuit extending from ground at RA2I0 byway of RA2|0, RA26I, RC262 and the winding of R210 to battery. Whenenergized over the above-traced circuit, the hold relay R210 operates tocomplete, at RA21I, a multiple path for applying ground potential to thecontrol conductor CI I8 of the trunk line I I5, to complete, at RA212, acircuit for energizing the winding on the core leg L261 of the field`structure of the test relay R265, to prepare, at RA213, a circuit,traced hereinafter, for energizing the winding on the core leg L268 ofthe fleld structure of the test relay R265, to interrupt, at RA214 andRC216, a further point in the previously mentioned circuit forenergizing the winding of the release magnet M230, and to prepare, atRA214 and RC215, a point in a circuit, traced hereinafter, forenergizing in multiple the lower winding of the transfer relay R290 andthe winding of the vertical magnet M236. The application of groundpotential to the control conductor CI I8 of the trunk line I I5completes a circuit for energizing the upper winding of the transferrelay R290, this circuit extending from the grounded control conductorCI I8 by way of the set of switch springs S211 and the upper winding ofR290 to battery. When energized over the above-traced circuit, thetransfer relay R290 operates to interrupt, at RA29I, a point in acircuit, traced hereinafter, for energizing the winding of the rotarymagnet M231 and to interrupt, at RA292, a point in the previouslymentioned circuit for energizing the winding of the release magnet M238.At this time, the selector switch 200 is conditioned to be responsive toa digit .aled thereinto, thereby to cause the wiper set if the Strowgermechanism 20| thereof to be driven away from its normal position in thevertical direction in a manner more fully described hereinafter.

Also, the start relay RI40 prepares, at RAI42, a circuit, tracedhereinafter, for energizing the second test relay R325 in thedistributor 300, interrupts, at RA|43, a point in a path tracedhereinafter for applying ground potential to the guard conductor C322,interrupts, at RAIN and RCI45, a point in the previously traced path forapplying ground potential in the finder switch |30 to the alltrunks-busyconductor 032|, prepares, at RAi'l, a circuit traced hereinafter forenergizing the winding of the rotary magnet MIN, and completes, at RAIB,a circuit for energizing the vertical magnet MI10. The circuit forenergizing the vertical magnet MI10 extends from ground, at RA352, byway of RA352, RA31i, RA36I, RC362, the wiper 304 and associated contactof the rotary switch 30|, the vertical conductor C320, RAI48, and thewinding of MI10 to battery. When energized over the above-tracedcircuit, the vertical magnet MI10 operates. Upon operating, the verticalmagnet MI10 drives the carriage of the Strowger mechanism |40 of thefinder switch |30 one step in the vertical direction and completes, atMAI10, a circuit for energizing the step relay R310 in the distributor300. The circuit for energizing the step relay R310 extends from ground,at MAI10, by way of MAI10, the interrupter conductor C3I9 and thewinding of R310 to battery.

' When energized over the above-traced circuit, the step relay R310operates to interrupt, at RA31 I, a point Vin the previously tracedcircuit for energizing the winding of the vertical magnet MI10, therebyto cause the vertical magnet MI10 to restore. Upon restoring, thevertical magnet MI10 interrupts, at MAI10, the previously traced circuitfor energizing the step relay R310, thereby to cause the latter relay torestore. Upon restoring, the step relay R310 completes, at RA31I, apoint in the previously traced circuit for energizing the winding of thevertical magnet MI10, whereupon the vertical magnet MI10 operates todrive the carriage of the Strowger mechanism |40 of the iinder switch|30 an additional step in the vertical direction and to recomplete, atMAI10, the previously traced circuit for energizing the step relay R310in the distributor 300.

The step relay R310 in the distributor 300 and the vertical magnet MI10in the iinder switch |30 continue to interact in the above-describedmanner, thereby to cause the carriage of the Strowger mechanism |40 ofthe iinder switch |30 to be driven step by step in the verticaldirection until the carriage wiper |41 engages a contact in the row ofcontacts associated therewith having marking ground potential thereon.In the present instance, the carriage of the Strowger mechanism |40 ofthe finder switch |30 is driven two steps in the vertical direction,whereupon the control wiper |41 engages the contact |48 in the row ofcontacts having marking ground potential thereon. A circuit is thencompleted for energizing the lower Winding of the transfer relay R360 inseries with the winding of the step relay R310, this circuit extendingfrom the grounded contact |48 in the row of contacts by way of thecontrol wiper |41, the rst test conductor C3I1, the wiper 302 andassociated contact of the rotary switch 30|, RA366, RC361, the lowerwind,- ing of R360, RA351, and the winding of R310 to battery. It isnoted that the above-traced circuit for energizing the lower winding ofthe transfer relay R360 in series with the winding of the step relayR310 is completed immediately the carriage of the Strowger mechanism |40of the finder switch |30 is driven the second step in the verticaldirection. Accordingly, the step relay R310 does not restore incident tothe restoration of the vertical magnet MI10 at this time.

Shortly after the transfer relay R360 is energized over the above-tracedcircuit it operates, this relay being of the slow-to-operate type. Uponoperating, the transfer relay R360 completes, at RA369, a holdingcircuit traced hereinafter for energizing the upper winding thereof,interrupts, at RA366 and RC361, a point in the previously traced circuitfor energizing the lower winding thereof in series with the step relayR310, and prepares, at RA366 and RC368, a circuit traced hereinafter forenergizing the first test relay R320. Also, upon operating, the transferrelay R360 interrupts, at RA365, a point in the previously tracedoriginal circuit for energizing the control relay R350 in series withthe winding of the 6 l rotary magnet M303, an alternative circuit forenergizing the control relay R350 in series with the winding of therotary magnet M308 being completed at this time; interrupts, at RAIBIand RC362, a further point in the previously traced circuit forenergizing the vertical magnet Ml10; and prepares, at RA36| and RC3, apoint in a circuit traced hereinafter for energizing the rotary magnetM|1|.

As previously noted, upon operating, the control relay R350 completes,at RA356. a point for energizing the timing relay R315, this circuitextending from ground, at RA356, by way of RA356, RA333, RC334, and thewinding of R315 to battery. When energized over the above-tracedcircuit, the timing relay R315 operates to complete, at RA316 and RC318,RC313, a circuit for energizing the control relay R380, this circuitextending from ground, at 'RA356, by way of RA356, RA316, RC318, RC319,and the winding of R380 to battery. Shortly after the control relay R380is energized by Way of the abovetraced circuit, this relay operates,this relay being of the slow-to-operate type. Upon operating, thecontrol relay R380 completes, at RA386, a holding circuit for energizingthe winding thereof, this circuit extending from ground, at RA356, byWay of RA356, RA316, RC318, RA386, and the winding of R380 to battery.Also, upon operating, the control relay R380 interrupts, at RA382 andRC383.- a point in a. circuit traced hereinafter for energizing theupper winding of the control relay R390, and prepares, at RA382 andRC384, a point in a holding circuit traced hereinafter for energizing.the upper winding of the transfer relay R360. Also, t'he control relayR380 completes, at RA38| the previously mentioned alternative circuitfor energizing the control relay R350 in series with the winding of therotary magnet M308, this circuit extending from ground, at RA38I, by wayof RA38I, RA359, the winding of R350, RA345, MA308, and t'he winding ofM308 to battery. Finally, upon operating, the control relay R380completes, at RA385, an obvious circuit for energizing the upper windingof thecontrol relay R330, thereby to cause the latter relay to operate.Upon operating, the control relay R330 completes, at RA336, a holdingcircuit for energizing the lower Winding thereof, this circuit extendingfrom ground at RA35| by way of RA35|, RA336, and the lower winding ofR330 to battery. Also, the control relay R330 interrupts, at RA330 andRC33I, a point in the previously traced original circuit for energizingthe control relay R350 in series with the winding of the rotary magnetM308, and completes, at RA330 and RC332, a multiple alternative circuitfor energizing the control relay R350 in series with the winding of therotary magnet M308. Furthermore, the control relay R330 interrupts, atRA333 and RC334, a point in the previously traced circuit for energizingthe timing relay R315; prepares, at RA333 and RC335, a point in thepreviously mentioned holding circuit for energizing the upper winding ofthe transfer relay R360; prepares, at RA331, a point in a circuit tracedhereinafter for energizing the first test relay R320; and prepares, atRA338, a point in a circuit traced hereinafter for energizing the secondtest relay R325.

When the previously traced circuit for energizing the timing relay R315is interrupted, the 1r-tter relay restores, thereby to cause-theweighted armature RA316 thereof to vibrate between the rssociatedcontacts RC311 and RC318, in order to. complete intermittently thepreviously traced holding circuit for energizing the control relay R380.It is noted that the weighted' armature RA310 vibrates between thecontacts noted for a predetermined time interval, thereby to retain thecontrol relay R380 in its operated position during this time interval.

The previously mentioned holding circuit for energizing the upperWinding of the transfer relay R360 extends from ground, at RA355, by wayof ,RA353, RA333, RC3, RA382, RC3, RAS, and

the upper winding of R360 to battery; while the previously mentionedcircuit for energizing the rotary magnet MI1| extends from ground, atRA352, by -way of RA352, RA31|, RA36I, RC3, RA32I, RC322, RA326, RC321,the rotary conductor C324, RAISS, RA| 51, RAI41, and the winding of M|1|.to battery. When energized over the above-traced circuit, t'he rotarymagnet M|1| operates to drive the carriage of the Strowger mechanism |40of the finder switch |30 one step in the rotary direction and tocomplete, at MA|1|, an alternative circuit for energizing the step relayR310 in the distributor 300. The circuit for energizing the step relayR310 extends from ground, at MA|1|, by way of MA|1|, the interrupterconductor C3l3, `and the winding of R310 to battery. When energized overthe abovetraced circuit, the step relay R310 operates to interrupt, atRA31|, a point in the previously traced circuit for energizing therotary magnet M I1|, thereby to cause the rotary magnet to restore. Uponrestoring, the rotary magnet M|1| interrupts, at MAI1I, the previouslytraced alternative'circuit for energizing the step relay R310, therebyto cause the step relay to restore and recomplete, at RA31|, thepreviously traced circuit for energizing the winding of the rotarymagnet Mill.

The step relay R310 in the distributor 300 and the rotary magnet M |1|in the finder switch |30 continue to interact in the manner describedabove until the carriage of the Strowger mechanism |40 of the finderswitch |30 is rotated in the rotary direction to the position of thecontact set terminating the calling subscriber line |0|, at which timethe wiper |43 of the upper wiper set engages the contact of the contactset terminating the control conductor CI04 of the subscriber line |0|,assuming that the line |0| is accessible to the upper wiper set of theStrowger mechanism |40 of the finder switch |30. whereupon a circuit iscompleted for energizing the winding of the cutoff relay RI I0 in theline circuit |00 inseries with the first test relay R320 in thedistributor 300. The last-mentioned circuit extends from ground at RA331by way of RA331, the unidirectional current conducting device or copperoxide rectifier 341, the winding of R320, RC368, RA366, the wiper 302and associated contact of the rotary switch 30|, the rst test conductorC3|1, the wiper |43 of the upper wiper set, the associated'contactterminating the control conductor CI04 of' the subscriber line 0|, CI04,RA|2| and the winding of the cutoff relay RI l0 to battery.

When the cutofl' relay RI I0 in the line circuit |00 is energized by wayof the above-traced circuit, it does not operate due to the high seriesresistance of the first test relay R320 in the distributor 300. However,the first test relay R320 does operate. Upon operating, the first testrelay R320 interrupts, at RA32| and RC322, a point in the previouslytraced circuit for energizing the Winding of the rotary magnet M|1I andcompletes, at RA32| and RC323, a circuit for ener- `switch gizlng theswitching relay R|60 in the finder |33. 'I'he circuitV for energizingthe switching relay R|60 extends from ground, at RA352, by way of RA352,RA31I, RA36I, RC36I, RA32I, RC323, the wiper 306 and associated contactofthe rotary switch 30|, the conductor C323, RAI55, and the winding ofR|60 to battery. When energized over the` above-traced circuit, theswitching relay R|60 operates to interrupt, at RAI65, a further point inthe previously traced circuit for energizing the winding of the rotarymagnet M|1| and to complete, at RAI64, a hold-` ing circuit forenergizing the winding thereof, this circuit extending from the groundedAconductor CI |8 by way of RAIN, and the winding of R|60 to battery.Also, upon operating, the switching relay R|60 connects the trunk line|3| terminated by the upper wiper set to the trunk line ||5 extendingbetween the finder switch |30 and the selector switch 200. Specifically,the conductors C|32, C|33 and C|34 of the trunk line |3| arerespectively connected, at RAIGi, RA|62 and RA|63, to the conductorsCIIG, C||1 and CIIB, respectively, of the trunk line I|5. When thegrounded control conductor CI|8 of the trunk line ||5 is connected tothe control conductor C|34 of the trunk line |3|, an alternative circuitis completed for energizing the cutol relay RI I0 in the line circuit|00, this circuit extending from the grounded control conductor CII 8 ofthe trunk line ||5 by way of RAI63, the control conductor C|34 of thetrunk line |3I, the wiper |43 of the upper wiper set, the associatedcontact terminating the control conductor CI03 of the subscriber line|0I, CIM, RAI2I, and the winding of R||0 to battery. When energized overthe above-traced circuit, the cutoi relay R||0 operates to complete, atRAI I3, a holding circuit for energizing the winding thereof, thiscircuit extending from the grounded control conductor CIM of thesubscriber line III by way of CIM, RA||3, and the winding of RI Il tobattery. Also, upon operating, the cutoi relay R||0 interrupts, at RAIand RAII2, points in the previously traced circuit i'or energizing theline relay R|20, thereby to free the subscriber line |0| of impedanceelements and to cause the line relay R|20 to restore. Also, uponoperating, the cutoff relay RI Il completes, at RAI I4, a circuit forenergizing the winding of the meter relay R|03 associated with the linecircuit |00, assuming that the upper terminal of the winding of themeter relay RIOS is connected to the conductor CI08. This circuitextends from the grounded control conductor CIII of the subscriber line|0| by way of RAII3, RAIIl, CI08, and the winding of R|03 to battery.Although the winding of the meter relay RIOS is energized, this relaydoes not operate at this time as this relay is of the marginal type.

When the line conductors C|32 and C|33 of the trunk line |3| areconnected to the line conductors CI I6 and C I1, respectively, of thetrunk line IIS, an alternative circuit is completed for energizing inseries the upper and lower windings of the line relay R260 in theselector switch 2li. This circuit extends from ground by Way of theupper winding of R260, RC2|6 and RA2|4 to the line conductor CI I1, andfrom battery by way of the lower winding of R260, RC2|3 and RA2|| to theline conductor C2|6, the line` conductors C2|6 and C2|1 of the trunkline 2|5 being connected together by Way of the bridge path connectedbetween the line conductors C|02 and CI03 of the subscriber line III atthe subscriber substation A.

It is noted that,A when'the carriage Aof the Strowger mechanism of theilnder switch |30 is operated away from its normal position the iirstAstep in the vertical direction, the sets of switch springs S|15 and S|19are actuated. More specifically, the switch springs |8| and |82 of theset of switch springs S|10 are actuated into disengagement; while theswitch springs |8| and |80 of the set of switch springs S|19 areactuated into engagement. When the switch springs |-8| and |80 of theset of switch springs S|19 are actuated into engagement, a point isprepared in a path traced hereinafter for applying ground potential tothe guard conductor C322. Also, the switch springs |18 and |11 of theset of switch springs SI are actuated into disengagement and the switchsprings |16 and |16 of the set of switch springs SI15 are actuated intoengagement. When the switch springs |18 and |11 of the set of switchsprings SI15 are actuated into disengagement, a further point in thepreviously traced path for applying ground potential to theall-trunks-busy conductor C32| is interrupted; and when the switchsprings |18 and |16 of the set of switch springs SI15 are actuated intoengagement, a point is prepared in a circuit traced hereinafter forilluminating the supervisory lamp L|28.

Also, upon operating, the switching relay R|60 in the iinder switch |30interrupts, at RA|66 and RC 68, a point in a circuit traced hereinafterfor energizing the release magnet MI12, and prepares, at RA|66 andRC|61, an additional point in the previously mentioned circuit forilluminating the supervisory lamp L|28. Furthermore, the switching relayR|60 interrupts, at RA|60, a point in a circuit traced hereinafter forenergizing the switching relay RI50, thereby to prevent operation of theswitching relay R|50 at this time; and completes, at RAISS, thepreviously mentioned path for applying ground potential to the guardconductor C322, this path extending from ground, at the switch spring|80 of the set of switch springs SI19, by way of the switch springs |80and |8| of the set of switch springs SI10, RAi69, and the switch springs|85 and |84 of the busy switch S|83 to the guard conductor C322. Thisapplication of ground potential to the guard conductor C322 completes acircuit for energizing the Winding of the rotary magnet M308 of therotary switch 30|, this circuit extending from the grounded guardconductor C322 -by way of the wiper 305 and associated contact of therotary switch 30|, RA353, RC355, and the winding of M308 to battery.When energized over the above-traced circuit, the rotary magnet M308operates, thereby to condition the wipers of the rotary switch 30| to bedriven one step in the' rotary direction. Also, upon operating, therotary magnet M308 interrupts, at MA308, a point in the previouslytraced alternative circuit for energizing the winding thereof in serieswith the winding of the control relay R350, thereby to cause the controlrelay R350 to restore.

Upon restoring, the control relay R350 interrupts,I at RA353 and RC355,a point yin the pre- Viously traced circuit for energizing the windingof the rotary magnet M308, thereby to cause the rotary magnet M308 torestore. Upon restoring, the rotary magnet'M308 drives the wipers 302 to301, inclusive, of the rotary switch 30|.one

step in the rotary direction and into engagement with the contacts inthe associated contact banks terminating the control conductorsextending to the nder switch of the next link. 'I'he subse` quentoperation of the distributor 300 depends upon the idle or busy conditionof the finder switch of the next link, in a manner more fully describedsubsequently.

Assumingthat there are no other calls in the ilrst group of lines atthis time, when the line relay R|20 of the line circuit |00 associatedwith the subscriber line restores it interrupts, at RAI25, thepreviously traced path for applying ground potential to the controlconductor C|90, interrupts, at RA|22 and RC|23, the previously tracedpath for applying ground potential to the control conductor C| of thesubscriber line |0I, and completes, at RA|22 and RC|24, an alternativepath for applying ground potential to the control conductor CI 05,thereby to mark 'the subscriber line I0| as busy to the connectorswitches having access thereto. 'I'he last-mentioned path extends fromthe grounded control conductor C|04 of the subscriber line |0| by way ofRAI I3, RCI 24 and RA|22, to the control conductor C|05.

When ground potential is removed from the control conductor C|90, thepreviously ytraced circuit for energizing the start relay R345 in thedistributor 300 is interrupted, thereby to cause the start relay R345 torestore. Upon restoring, the start relay R345 interrupts, at RA346, thepreviously traced original circuit the control relay R350 in series withthe winding of the rotary magnet M300. Also, when the control relay R350restores, as previously noted, it interrupts, at RA359, a further pointin the circuit for energizing the winding thereof in series with thewinding of the rotary magnet M308. Also, at RA353 and RC354, the wiper305 of the rotary switch 30| is connected by way of theself-interrupting contact MA308 and the winding of the rotary magnetM308 to battery, this connection extending from the wiper 305 by way ofRA353, RC354, RA345, MA308, and the winding of M300 to battery.

In the event the nder switch of the next link in the rst group is busyat this time, ground potential appears upon the guard conductor thereof,corresponding to the guard conductor C322 of the finder switch |30, aspreviously noted, thereby to complete a circuit extending by way of thepreviously traced connection for energizing the winding of the rotarymagnet M308. When thus energized, the rotary magnet M308 operatestocondition the wipers of the rotary switch 30| to be driven anadditional step in the rotary direction and to interrupt, at MA308, thepreviously traced circuit for energizing the winding thereof. When thepreviously traced circuit for energizing the winding of the rotarymagnet M308 is interrupted, the rotary magnet restores, thereby to drivethe wipers of the rotary switch 30| an additional step in the rotarydirection. The rotary magnet M308 continues to operate in theabove-described manner in order to cause the wipers of the wiper set 30|to be driven step by step in the rotary direction until the nder switchin an idle link of the rst group is found. When the finder switch of anidle link of the first group is found, further operation of the rotarymagnet M300 is interrupted, due to the fact that no ground potentialappears upon the guard conductor thereof, corresponding to the guardconductor C322 of the nder switch |30.

for energizing Accordingly, the distributor 300 operates automaticallyto preselect an idle link in the first group of links immediately afterthe previously selected link in the first group of links is taken foruse by a calling line and operates to nnd the calling line.

It is noted that the distributor 300 operates in the above-describedmanner in order to preselect an idle link in the nrst group of linksonly in the event that idle link is available in the first group oflinks, due to the fact that the busy transfer relay R340 is retained inits operated position at this time only in the event that groundpotential is present upon the all-trunks-busy conductor C32|, whichcondition obtains only in the event that there is an idle link availablein the rst group of links. In the event that all of the links in theilrst group of links are busy at this time, no ground potential appearsupon the all-trunks-busy conductor C32I, whereby the circuit forenergizing the busy transfer relay R340 is interrupted in order tocause' the'busy transfer relay R340 to restore. Upon restoring, the busytransfer relay R340 interrupts, at RA344, a further point in thealternative holding circuit for energizing the winding thereof,interrupts, at RA345, a point in the previously traced circuit forenergizing the winding of the rotary magnet M308, thereby to preventoperation of the rotary magnet M300, and interrupts, at RA34| and RC343,the connection b etween the start conductor C3|6 and the Winding of thestart relay R345. Also, upon restoring, the busy transfer relay R340connects, at RA34| and RC342, the conductors C328 and C321 extending tothe distributor 3| 2. Accordingly, at this time, the start conductorC3|6 extending to the distributor 300 is connected, together with thestart conductor C3l5, to the conductor C321 extending to the distributor3|2. Hence, at this time, the distributor 3|2 is operative to assignidle links in the second group of links to the use of calling lines inboth the first and second groups of lines.

Continuing now with the release of the distributor 300 incident to therestoration of the start relay R345 and the control relay R350, when thecontrol relay R350 restores it interrupts, at RA35I, the previouslytraced circuit for energizing the start relay R|40 in the finder switch|30. Shortly thereafter the start relay R|40, being of theslow-to-release type, 'restores to interrupt, at RAMI, themst-'mentioned path between the line conductors C||6 and. CIII of thetrunk line 5 and to complete, at RAI43, an alternative path for applyingAgli und potential to the guard conductor C322, is path extending fromground, at the switch spring |00 of the set of switch springs S|`|9 byway of the switch springs |00 and |0| of the set of switch springs SHS,RAI43, and the switch springs |05 and |04 of the busy switch S|03 to theguard conductor C322. This application of ground potential to the guardconductor C322 insures that the distributor 300 will not operate toselect the busy link 60 at this time. Also, upon restoring, the startrelay R|40 interrupts, at RAI", a further point in the previously tracedcircuit for energizing the rotary magnet Ml 1|, interrupts,

at RA|40, a further point in the previously traced circuit forenergizing the vertical magnet MI10, interrupts, at RAI42, a point inthe previously mentioned circuit for energizing thesecond test relayR325 in the distributor 300, and completes, at RA|44 and RC |45, thepreviously mentioned circuit for illuminating the supervisory lamp L|28, this circuit extending from ground,-at RAI, by way of RAI, RCHS,ythe switch springs |86 and |81 of the busy switch S|83, the switchsprings |18 and |16 of the set of switch springs SI15, RA|66, RC|61 andL|28 to battery. The illumination of the supervisory lamp L|28 indicatesto the exchange attendant that., the link 60 is busy upon a call routedtherethrough from a line included in the rst group of lines.

Also, upon restoring, the control relay R350 in the distributor 300interrupts, at RA352, the previously traced original circuit forenergizing the switching relay R|60 in the nder switch |30,

interrupts. at RA351, a further point in the previously traced circuitfor energizing the lower wind-ing of the transfer relay R360 in thedistributor 300, and interrupts, at RA356, a point in the previouslytraced circuit for energizing the upper winding oi' the transfer relayR360 and a point in the previously traced holding circuit for energizingthe winding of the control relay R380, thereby to cause the transferrelay R360 and the control relay R380 to restore. Upon restoring, thetransfer relay R360 interrupts, at RA369., a further point in theholding circuit for energizing the upper winding thereof, interrupts, atRA366 and RC368, a point in the previously traced circuit for energizingthe first test relay R320, and prepares, at RA36-6 and RC361, a point inthe previously traced circuit for energizing the lower winding thereof.Also, upon restoring, the transfer relay R360 prepares, at RA365, apoint in the previously traced original circuit for energizing thewinding of the control relay R350 in series with the winding of therotary magnet M308, interrupts, at RA36| and RC364, a further point inthe previously traced circuit for energizing the switching relay R|60 inthe nder switch |30, and prepares, at RA36| and RC362, a point in acircuit for energizing the vertical magnet in the finder switch of aselected link when thel distributor 300 operates to select an idle linkin the first group of links to the use of a calling line.

Upon restoring, the control relay R380 interrupts, at RA386, a furtherpoint in the holding circuit for energizing the winding thereof,interrupts, at RA385, a point in the holding circuit for energizing theupper winding of the control relay R330, thereby to cause theflatterrelay to restore, and interrupts, at RA382 and RC384, a further point inthe holding circuit for energizing the upper winding of the transferrelay R360. Also, the control relay R380 prepares, at RA382 and RC383, apoint in a circuit traced hereinafter for energizing the upper windingof the control relay R390, and interrupts, at RA38I, a point in thepreviously traced alternative circuit for energizing the winding of thecontrol relay R350 in series with the winding of the rotary magnet M308.

Upon restoring, the control relay R330 interrupts, at RA336, a furtherpoint in the previously traced holding circuit for energizing the 'lowerwinding thereof, interrupts, at RA331, a further point in the previouslytraced circuit for energizing the first test relay R320, and interrupts,at RA338, a point in thepreviously mentioned circuit for energizing thesecond test relay R325. Also, the control relay R330 interrupts, atRA333 and RC335, a further point in the holding circuit for venergizingthe upperV winding of the transfer relay R360, prepares, at RA333 andvRC334, a point in the previously traced circuit for energizing thetiming relay R315, interrupts, at RA330 and RC332,\a further point inthe pre;

viously traced alternative circuit for energizing the winding of thecontrol relay R330 in series with the winding of the rotary magnet M308,and prepares, at RA330 and RC33I, a point in the previously tracedoriginal circuit forenergizing the winding of the control relay R350 inseries with the winding of the rotary magnet Upon restoring, the firsttest relay R320 interrupts, at RA32| and RC323, a further point in thepreviously traced original circuit for energizing the switching relayR|60 in the finder switch- |30, and prepares, at RA32| and RC322, apoint in a circuit for energizing the rotary magnet in the finder switchof a preselected unir. At this ume'tne distributor soo lis completelyreleased for further use and the subscriber substation A isoperatively'connected by Way of the previously traced circuit to theselector switch 200.

As previously noted, as soon as the finder switch |30 operates to seizethe calling subscriber line ground potential; is applied therein to theguard conductor C332, thereby to complete the previously traced path forshort-circuiting the winding of the control relay R350 in order to causethe controlrelay R350 to restore and initiate the release of thedistributor 300. It is noted that it is not possible to reoperate therelay R350 unil the distributor 300 is completely released in spite ofthe fact that there may be present a calling line in the first group oflines. which causes the start relay R315 to remain in yits operatedcondition, due to the fact that, upon restoring, the control relay R350interrupts, at RA358, the previously traced alternative circuit forenergizing the winding thereof in series with the winding of the rotarymagnet M308, and the original circuit for energizing the winding of thecontrol relay R350 in series with the Winding of the rotary magnet M308is not recompleted until subsequent to the restoration of the transferrelay R360 and the control relay R330, as previously explained.Accordingly, the distributor 300 is complet-ely released each time afinder switch of a link selected thereby operates to nd a calling linein spite of the fact that the start relay R345 therein remains operated,due to the presence of other calling lines in the iirst group of lines.

In the event another calling line is present in the iirst group of linesat this time, the start relay R345 in the distributor 300 remains in itsoperated position, and, when the transfer relay R360 and the controlrelay R330 restore, the previously traced original circuit forenergizing the control relay R350 is recompleted, assuming that therotary magnet M308 has already operated to cause the rotary switch 30|to find an idle link in the rst group of links. 'Ihe control relay R350then operates, thereby to cause the nder switch of the previouslyselected link to operate and seize the calling subscriber line in thefirst group of lines, as explained above.

As previously noted, the distributor 300 is operative to cause thefinder switch of a selected link in thel first group of links, such asthe finder switch |30 of the link 60, to operate and seize a callingline in the second group of lines, which condition may arise when all ofthe links in the second group of links are busy. In this event, thedistributor 3|2 operates.r thereby to cause the conductors C321 and C328therein to be connected together, in a manner similar to that previouslyexplained, incident to the restoration of the busy transfer relay R340in the distributor 300 when all of the links in the ilrst group of linksare busy. At this time, ground potential applied to the start conductorC3|5 is extended by way of the conductor C321 and the distributor 3| 2to the conductor C320, in order to cause the start relay R345 in thedistributor 300 to be energized and to operate in the previouslydescribed manner. The subsequent operations of the distributor 300 andthe ilnder switch |30 of the link 00, incident to the operation of thestart relay R345 in the distributor 300, are the same as previouslyexplained, assuming that the calling line in the second group of linesis also accessible to the upper wiper set of the Strowger mechanism 40of the flnder switch |30.

Furthermore, the iinder switch 30 of the link 60 is operative in amanner substantially identical to that previously explained to find acalling line in `either `the rst group of linesor the second group oflines and accessible to the lower wiper set of the switching mechanism|40 thereof. However, in this case, when the carriage of the Strowgermechanism |40 of the nder switch |30 is rotated in the rotary directionto the position of the contact set terminating the calling subscriberline, battery potential is encountered by the wiper |46 in the lowerwiper set appearing upon the contact terminating the control conductorof the calling subscriber line. This application of battery potential tothe wiper |46 completes the previously mentioned circuit for energizingthe second test relay R325 in thedistributor 300, this circuit extendingfrom ground at RA338 by way of RA338, the unidirectional currentconducting device or copper oxide rectiiler 343, the winding of thesecond test relay R325, the second test conductor C326, RAI 42, and thecontrol conductor C'I38 of the trunk line |35 to battery potentialappearing upon the wiper |45. When energized over the above-tracedcircuit, the second test relay R325 operates to interrupt, at RA326 andRC32I, a point in the previously traced circuit for energizing therotary magnet M|'|| in the finder switch |30, thereby to arrest furtheroperation of the ilnder switch. Also, upon operating, the second -testrelay R325 completes, at RA325 and RC320, the previously mentionedcircuit for energizing the switching relay R|50 in the nder switch |30,this circuit extending from ground, at RA352, by way of RA352, RA3||,RA30I, RC3, RA32I, RC322, RA326, RC320, the wiper 301 and associatedcontact of the rotary switch 30|, the conductor C325, RAIGO, and thewinding of R|50 to battery. When energized over the above-tracedcircuit, the relay R|50 operates to interrupt, at RA|5'|, a furtherpoint in the previously traced circuit for energizing the rotary magnetMITI, and to complete, at RAISE, a path for applying ground potential tothe guard conductor C322. The path for applying ground Potential to theguard conductor C322 extends from ground, at the switch spring |00 ofthe set of switch 'springs SH3, by way of the switch springs |00 and |0|of the set of switch springs SI10, RAI53, and the switch springs |05 and|04 of the busy switch S|03 to the guard conductor C322. 'I'hisapplication of ground `potential to the guard conductor C322 causes thedistributor 300 to be released and the rotary switch 30| therein toOperate and select an idle link in the ilrst group of links, aspreviously explained.

Also, upon operating, the switching relay R|50 interrupts, at RAI, apoint in the previously traced pleteS,

ilnder switch |30,

circuit for energizing the switching relay R|00, and completes, at RAIN.a holding circuit for the winding thereof, this circuite from thegrounded control conductorC|`|0 oi! the trunk line v'III by way oi'RAI54. and the winding of R|50 to battery. Finally. the switching relayR|50 connects, the trunk line |30 extending to the lower wiper set ofthe Strowger m |40 to the trunk line H5. More specitlcally, theconductors C|30, CI3'| and CI30 of the trunk line |35 are respectivelyconnected, at RAIII, RAIIZ and RAIN, to the conductors C||0, C||`| andCH3, respectively, of the trunk line H5. When the trunk line |35 isconnected to the trunk line III, the line circuit individuallyassociated with the calling subscriber line and the selector switch 200operate in the previously described manner.

It is noted that there is a possibility that the upper and lower wipersets of the Strowger mechanism |40 of the ilnder switch |30 maysimultaneously encounter contact sets in the contact bank terminatingcalling subscriber lines. In this event, the presence of batterypotential appearing upon the contacts in the two contact setsrespectively engaged by the wipers |43 and |46 in the upper and lowerwiper sets, respectively, of the Strowger mechanism |40 complete the'previously traced circuits for respectively energizing the windings ofthe ilrst and second test relays R320 and R325, respectively, thereby tocause both of these test relays to operate. Upon operating, the ilrsttest relay R320 comat RA32| and RC323, the previously traced circuit forenergizing the switching relay R|60, thereby to cause the switchingrelay R|60 to operate, and interrupts, at RA|2| and RCIZZ, thepreviously traced circuit for energizing the switching relay R|50,thereby to prevent operation of the switching relay Rl50. Accordingly,under this' conditio the switching relay R|00 is operated and theswitching relay R|50 is not operated. Hence, the ilnder switch |30operates to iind the calling line accessible to the upper wiper set ofthe Strowger mechanism |40 thereof in preference to the calling lineaccessible to the lower wiper set of the Strowger mechanism |40 thereof.

It is noted that, incident to operation of the the wipers |43 and |40 inthe upper and lower wiper sets, respectively, oi.' the Strowgermechanism |40 may engage contacts in the associated contacts of contactsets in the associated contact bank terminating the control conductorsof subscriber lines having either ground or booster battery potential"appearing thereupon; ground potential appearing upon the controlconductors of the subscribers lines when the subscriber lines are bustery,` potential appearing upon lines when the subscriber lines arebeing metered. When the wiper |43 or the upper wiper set of the Strowgermechanism |40 engages a contact having ground potential appearingthereupon, a path is completed for short-circuiting the winding oi therst test relay R320 in the distributor 300, this circuit extending fromthe grounded control conductor of the subscriber line, by way of thewiper |43 and associated contact, Cl33, the rst test conductor C3|'|,the wiper 302 and associated contact of the rotary switch 30|, RA300,RC3, the winding of R320, the copper oxide rectifier 341, and RA33`| toground. When the wiper |43 oi.' the upper wiper set of the Strowgermechanism |40 engages a contact having boosterbattery potentialappearing thereupon, a circuit winding of R390 to over the above-tracedcircuit, the control relayy is completed substantially identical to theabovetraced path, tending to energize the winding of the iirst testrelay R320. However, the copper oxide rectiiier 341 is so connected andarranged that current is prevented from traversing this circuit inadirection extending from the wiper |43 to ground at RA331. Accordingly,the first test| relay R320 is not effectively energized. Thus, the iirsttest relay R320 does not operate when the wiper |43 of the upper wiperset of the Strowger mechanism |40 engages a Contact terminating thecontrol conductor of a subscriber line having either ground or boosterbattery potential appearing thereon.

In a similar manner, a path is completed for short-circuiting thewinding of the second test relay R325 when the wiper |46 in the lowerwiper set of the Strowger mechanism |40 engages a contact terminating acontrol conductor of a subscriber line having ground potential appearingthereon; and a circuit is completed tending to energize the winding ofthe second test relay R325 when the wiper |46 engages a contactterminating a control conductor of a subscriber line having boosterbattery potential appearing thereon. However, the copper oxide rectifier348 prevents the winding of the second test relay R325 from beingeffectively energized in the last-mentioned case. Hence, thearrangements of the copper oxide rectifiers 341 and 348 in the circuitsfor respectively energizing the windings of the first and second testrelays R320 and R325, respectively, prevent false operation of theiinder switch |30 and the consequent seizure thereby of abusy'subscriber line having booster battery potential appearing upon thecontrol conductor thereof.

In the foregoing description of the operation of the finder switch |30of the link 60 to seize the calling subscriber line |0I, it was assumedthat the finder switch |30 operated properly to seize this callingsubscriber line. However, it may occur that the finder switch |30 failsto operate properly to seize the calling subscriber line I0| when theoperation thereof is initiated by the distributor 300, due to the factthat the finder switch |30 has become temporarily inoperative. In thisevent, the inder switch |30 fails to seize the calling subscriber line|0I. Accordingly, ground potential is not applied in the finder switch|30 to the guard conductor C322 in order to cause the distributor 300 tobe released, as previously explained. Hence, after a predetermined timeinterval, the vibratory armature RA316 of the timing relay R315 in thedistributor 300 assumes an intermediate position between the associatedcontacts RC311 and RC318, thereby to interrupt the previously tracedholding circuit for energizing the control relay R300 in order to causethe control relay R380 to restore. Upon restoring, the control relayR380 interrupts, at RA382 and RC384, the previously traced holdingcircuit for energizing the upper winding of the transfer relay R360,'andcompletes, at RA382 and RC383, a. point in the previously mentionedcircuit for energizing the upper winding of the control relay R390. Thecircuit for energizing the upper winding of the control relay R390extends from ground, at RA356, by way of RA356, RA333, RC335, RA382,RC383, and the upper battery. When energized R390 operates to complete,at RA392, a holding circuit for energizing the lower winding thereof,this circuit extending from the grounded conductor C330 by way of theswitch springs 330 and 331 of the busy switch S334, RA302, and the lowerwinding of R390 to battery. It is noted that ground potential appearsupon the conductor C330 in the distributor 3|2 so long as groundpotential appears upon the all-trunks-busy conductor associated with thender switches of the links in the second group of links, just as groundpotential appears upon the conductor C323 in the distributor 300 so longas ground poential appears upon vthe all-trunks-busy conductor'CSIlassociated with the finder switches of the links in the rst group oflinks. Also, upon operating, the relay R390 completes, at RA39I, a pathfor short-circuiting the winding of the control relay R350, this pathextending from the upper terminal of the winding ofV R350, by way ofRA39I, RA353, RC355, MA308, RA345, and the winding of R350 to the upperterminal thereof. When the winding of the control relay R350 isshort-circuited, it restores to interrupt, at RA353 and RC355, a pointin the previously traced path for short-circuiting the winding thereof,and to complete, at RA353 and RA354, an alternative path forshort-circuiting the winding thereof. The alternative path forshort-circuiting the winding of the control relay R350 extends from theupper terminal of the winding of R350 by way of RA39I, RA353, RC354, andthe winding of R350 to the upper terminal thereof. Also, upon restoring,the control relay R350 interrupts, at RA358, a point in the previouslytraced alternative circuit for energizing the winding of the busytransfer relay R340.

Also, upon operating, the control relay R390 interrupts, at RA333, thepreviously traced original circuit for energizing the winding of thebusy transfer relay R340, and interrupts, at RA334, the normalconnection between the conductor C329 extending into the distributor 3|2 and the winding of the busy transfer relay R340, thereby to cause thebusy transfer relay R340 to restore and to insure that it remains in itsrestored position. Upon restoring, the busy transfer relay R340completes, at RA34| and RC342, the previously mentioned connectionbetween the conductors C321 and C328 extending to the distributor 3|2,thereby to cause the distributor 3| 2 to assign links in the secondgroup of links to the use of calling lines in both the rst and secondgroups of lines, as previously explained.

Also, upon operating, the control relay R380 completes, at RA392, acircuit forilluminating the supervisory lamp L300, this circuitextending from the grounded conducor C330 by way of the switch springs338 and 331 of the busy switch S334, RA392, and the lamp L303 tobattery. Illumination of the supervisory lamp L30! indicates to theexchange attendant that the distributor 300 is locked out of service.The release of the remainder of the operated relays in the distributor300, incident to the restoration of the control relay R350 and the busytransfer relay R340, is the same as that previously described. At thistime, the distributor 300 is locked out of service, as previously noted.

It is noted that the distributor 300 remains locked out of service untilthe busy switch S334 is operated away from its normal position andreturned thereto, which switch will not be thus operated until thedefective iinder switch of one of the unks in the erst group of links isfound and again placed in working order. When the busy switch S334 isoperated away from its normal position, the switch springs S331 and S333are actuated into disengagement, thereby to interrupt the previouslytraced holding circuit for energizing the lower winding' of the controlrelay R390 in order to cause the control relay R390 to restore. Uponrestoring, the control relay R390 reconnects, at RA394, the conductorC328 extending into the distributor 3|2 to the winding of the busytransfer relay R340, and prepares, at RA393, a. point in the previouslytraced original circuit for energizing the winding of the busy transferrelay R340 by way of the al1-trunksbusy conductor C32 I is returned toits normal position, there is completed at the switch springs 335 and338 thereof the previously traced original circuit for energizing thewinding of the busy transfer relay R340 by way of the all-trunks-busyconductor rC32I, in the event one of the links in the first group oflinks is idle at this time, as previously explained.

It is notedthat the ilnder switch |30 of the link 60 embodies anarrangement for causing the distributor 300 to select another idle linkin the iirst group of links for the use of the calling subscriber line|0| in the event that the nder switch |30 of the selected link 60 in therst group of links fails to find the calling line |0| incident to theoperation thereof.` More particul-arly, the set of switch springs S|14in the iinder switch |30 is actuated into engagement when the carriageof the Strowger mechanism |40 of the finder switch |30 is driven elevensteps in the rotary direction away from its normal position, due to thefailure of the inder switch |30 to iind the calling line 0 I. When theset of switch springs S|14 is actuated into engagement, a path iscompleted for applying ground potential to the guard conductor C322,this path extending from ground, at the set of switch springs SI14, byway of the set of switch springs SI14, the switch springs |85 and |84 ofthe busy switch S|83 to the guard conductor C322. This application ofground potential to the guard conductor C322 completes the previouslytraced circuit for energizing the winding of the rotary magnet M308 andfor short-circuiting the winding of the control relay R350, thereby tocause the distributor 300 to release and to cause the rotary switch 30|therein to operate and select another idle link in the rst group oflinks for the use of the calling subscriber line I0|, in the previouslydescribed manner.

It is noted that the nder switch 30 of the link 60 may be rendered busy.by operating the busy switch SI83. When the busy switch SI 83 isoperated, the switch springs |86, |81 and |84, |85 thereof are actuatedinto disengagement, and the switch springs |86, |84 thereof are actuatedinto engagement. When the switch springs |86 and |81 of the busy switchS|83 are actuated into disengagement, the previously traced path forapplying ground potential in the nder switch |30 to the all-trunks-busyconductor C32| is lnterrupted; when the switch springs |84 and |85 ofthe busy switch SI83 are actuated into disengagement, a point in thepreviously traced path for applying ground potential to the guardconductor C322, incident to the operation of the switching relays R|50and RISO, is interrupted; and, when the switch springs |86 and |84 ofthe busy switch S 83 are actuated into engagement, a path is completedin the nder switch |30 for applying ground potential to the guardconductor C322. The last-mentioned path for applying ground potential tothe guard conductor C322 When the busy switch S334,y

extends from ground, at RAI, .by way oi.' RAI 44, RCI45, and the switchsprings |08 and |84 oi.' the busy switch SI83, to the guard conductorC322. This application of ground potential to the guard conductor C322marks the link 80 as busy, thereby to prevent the distributor 300 fromselecting the link 80 in the ilrst group of links, or causes the rotaryswitch 30| in the distributor 300 to operate and select another idlelink in the rst group oi' links in the event that the distributor 300has previously operated to select the link 00 prior to the operation oi'the 4busy switch SI83 therein. .In the event the distributor 300 hasoperated to select the link 60 in the ilrst group of links prior to,operation of the busy switch SI83 therein, as explained abov theapplication of ground potential to the guard conductor C322, incident tothe operation of the busy switch SI83, causes the rotary switch 30| inthe distributor 300 to operate and select another idle link in the firstgroup of links. Speciilcally, this application of ground potential tothe guard conductor C322 completes the previously traced circuit forenergizing the winding of the rotary magnet M308 of the rotary switch30| in the distributor 300. The operation of the rotary magnet M308 tocause the rotary switch 30| to select an idle link in the ilrst group oflinks is the same as that previously explained.

As previously noted, an arrangement is provided for testing'theoperation of the distributor 300 and the finder switches of the linksassociated therewith. This arrangement comprises the busy switch S334and the test jacks J33I, J332 and J333. In order to test the operationof the distributor 300 to select idle links in the ilrst group of linksand to test the operation of the selected links in the rst group oflinks, the busy switch S334 is operated away from its normal positionand plugs are inserted into the jacks J33| and J332. When the busyswitch S334 is operated away from its normal position, a point in thepreviously traced holding circuit for energizing the lower winding ofthe control relay R390 is interrupted at the switch springs 331 and 338thereof, and the previously traced original circuit for energizing thewinding of the busy transfer relay R340 is interrupted at the switchsprings 335 and 336 thereof. The busy transfer relay R340 thenrestoresto interrupt, at RA344, a further point in the previously tracedalternative holding circuit for energizing the winding thereof, tointerrupt, at RA345, a point in the previously traced circuit forenergizing the winding of the control relay R350 in series with thewinding of the rotary magnet M308, to interrupt, at RA34| and RC343, apoint inthe previously traced circuit for energizing the start relayR345, and to complete, at RA34| and RC342, a connection between theconductors C328 and C321 extending into the distributor 3|2. Aspreviously noted, when the conductors C321 and C328 are connectedtogether, the distributor 3| 2 is operative to assign idle links in thesecond group of links to the use of calling lines in both the rst andsecond groups oi' lines. Accordingly, the test of the distributor 300 atthis time does not interrupt trailc on the subscriber lines in the rstgroup of lines. When the plug is inserted into the jack J 33| analternative circuit, traced hereinafter, is prepared for energizing thewinding of the control relay R350 in series with the winding of therotary magnet M308; and, when the' plug is inserted into the jack J332,an alternative circuit is completed for energizing the winding of thestart relay R345. The last-mentioned circuit extends from ground by wayof the jack J 332 and associated plug, the resistor 339, and the windingof R345 to battery. When energized over the above-traced circuit, thestart relay R345 operates to complete, at RA346, the previouslymentioned alternative circuit for energizing in series the winding ofthe control relay R350 and the winding of the rotary magnet M308, thiscircuit extending from ground, at RA330, by way of RA330, RC33I, RA365,RA346, the winding of R350, the jack J33| and. associated plug, MA308,

and the winding of M308 to battery. When energized over the above-tracedcircuit, the control relay R350 operates. However, the rotary magnetM308 does not operate due to the high series resistance of the windingof the control relay R350.

Upon operating, the control relay R350 prepares, at RA351, a point inthe previously traced circuit for energizing the lower winding of thetransfer relay R380, and completes, at RA356, the previously tracedcircuit for energizing. the winding of the timing relay R315, thereby toinitiate the timing operation of the relay R315 and the control relaysR380, R390 and R330 in the previously described manner. Also, uponoperating, the control relay R350 prepares, at RA359, a point in analternative circuit for energizing the winding thereof in series withthe Winding of the rotary magnet M308; prepares, at RA353 and RC355, apoint in the previously traced circuit for energizing the winding of therotary magnet M308 directly from the guard conductor C322; prepares, atRA352, a point in the previously traced circuit for energizing thevertical magnet of the iinder switch of the selected link, andcompletes, at RA35|, the previously traced circuit forenergizing thestart relay of the nder switch of the selected link. Assuming that therotary switch 30| has previously operated to select the link 60, whenthe control relay R350 operates it completes, at RA35|, the previouslytraced circuit for energizing the start relay RI 40 in the nder switch|30 of the link 60. Upon operating, the start relay R|40 completes, atRAI48, the previously traced circuit for energizing the vertical magnetM|10, thereby to initiate operation of the finder switch |30, in thepreviously described manner. 'I'he vertical magnet M|10 and-the steprelay R310 in the distributor 300 interact in the previously describedmanner, thereby to cause the carriage of the Strowger mechanism |40 ofthe finder switch |30 to be driven step by step in the verticaldirection. In the event that there is la calling line in either thefirst or second group of lines at this time, the finder switch |30operates, in the previously described manner, in order to seize thecalling subscriber line. However, in the event there is no calling lineat this time in either the iirst or second group of lines, the carriageof the Strowger mechanism |40 of the nder switch |30 is i'lrst driven'in the vertical direction ten steps away from its normal position,whereupon the control wiper |41 associated with the row of contactsengages the grounded contact |48', thereby to complete the previouslytraced circuit for energizing the lower wrindingof the transfer relayR360 in order to cause the transfer relay R360 to operate. Uponoperating, .the transfer relay R360 completes, at RA36| and RC364, thepreviously traced circuit for energizing the rotary magnet M|1|. Therotary magnet M|1| then operates to drive the carriage of the Strowgermechanism |40 in the finder switch |30 step by step in the rotarydirection eleven steps away from its normal position, whereupon the setof switch springs S|`|4 is actuated into engagement. When the sct ofswitch springs -S|`|4 is actuated into engagemennthe previously tracedpath for .applying ground potential to the y `guard conductor-C322 iscompleted, thereby to cause the distributor 300 to release and to causetherotary switch 30| to operate and select another idle link in theflrst group of links in the previously described manner. When anotheridle link in the first group of links is selected in the previouslydescribed manner, the distributor 300 again operates to cause the nderswitch of this link either to seize a calling vline in the iirst orsecond group of lines or to be operated, in the above-described mannerThe distributor 300 and the idle links in the first group of links arereoperated in the above-described manner so long as the busy switch S334remains operated away from its normal position and the plugs areretained irl the jacks J 33| and J 332. In o-rder to restore theoperation of the distributor 300 to normal, the busy switch S334 isreturned to its normal position and the plugs are removed from theIjacks .133| and .1332.

Inorder to test the timing operation of the distributor 300, plugs areinserted into the jacks J 332 and J 333, while the busy switch S334remains in its normal position. When the plug is inserted in the jack J332, the previously traced alternative circuit for energizing the startrelay R345 is completed; and, when the plug is inserted into the jack J333, an alternative circuit is completed for energizing the winding ofthe step relay R310. 'I'he last-mentioned circuit extends from ground byway of the jack J 333 and associated plug, and the Winding of R310 tobattery. When energized over the above-traced circuit, the step relayR310 operates to interrupt, at RA31I, a point in the previously tracedcircuit for energizing the vertical magnet of the nder switch of theselected link, thereby' to prevent operation of the finder switch of theselected link, The operation of the start relay R345 causes operation ofthe control relay R350, `as previously explained. Upon operating, thecontrol relay R350 completes, at RA356, the previously traced circuitfor energizing the timing relay R315, which latter relay operates tocomplete, at RA316 and RC318, RC319, the `previously traced circuit forenergizing the winding of the control relay R380, thereby to cause thelatter relay to operate shortly thereafter. Upon operating, the controlrelay R380 completes, at RA385, the previously traced circuit forenergizing the upper winding of the control relay R330, thereby to causethe latter relay to operate. Upon operating, the control relay R330completes, at RA336, the previously traced holding circuit forenergizing the lower winding thereof, and interrupts at RA333 and H0336,the previously traced circuit for energizing the timing relay R315,thereby to cause the latter relay to restore. Upon restoring, theYtiming relay R315 sets the weighted armature RA316 into operation,thereby to retain the control relay R380 in its operated position for apredetermined interval, after which the relay R380 restores, Uponrestoring, the control relay R380 completes, at'RA382 and RC383, thepre- Vviously traced circuit for energizing the upper trol relay R330locks the distributor 300 outoi service and the illumination of thesupervisory lamp L30! indicates to the exchange attendant this conditionof the distribuer 300, as previously explained. l

. In order to restore normal operation of the distributor 300, the plugsare removed from. the jacks -I332 and J333, and the busy switch S330 isoperated away from its normal position and then returned to its normalposition, as previously explained.

Continuing now with the operation of the selector switch 200 to extend acall from the subscriber substation A to the subscriber substation B,when the finder switch |30 operates to seize the calling subscriber line|0|, the selector switch 200 is rendered operative in response toimpulses transmitted thereto from the subscriber substation A. At thistime, the line relay R260, the hold relay R210 and the transfer relayR290 in the selector switch 200 occupy their operated positions, aspreviously explained.

It is noted that the test relay R265 in the selector switch 200 is ofthe shunt ileld type and comprises a ileld structure including an L-shaped leg L266, -two core legs L261 and L263, a shunt leg L269 and amovable armature RA265, two windings being respectively carried on thecore legs L261 and L266. 'I'he test relay R265 is so connected andarranged that, when the winding on the core leg L261 is energized, amagnetic ilux is produced in the field structure which traverses a firstmagnetic path extending from the core leg L261 by way of the base of theleg L266, the core leg L266, and the shunt leg L269 to the core legL261, thereby to polarize .the eld structure of the test relay R265.When the winding on the core leg L266 is energized with current of onepolarity, an additional magnetic flux is produced in the eldAccordingly, the armature RA265 of the test relay R265 is not operatedwith respect to the eld structure thereof. On the .other hand, when thewinding on the core leg 1.268 is energized with current of the oppositepolarity, a magnetic flux is produced in the shunt leg L269 which is inopposition to the magnetic flux traversing the shunt leg L26! by way ofthe iirst magnetic path. Accordingly, the magnetic ux produced by thewinding on the core leg L261 of the i'leld structure is diverted fromthe shunt leg L269 into a second magnetic path extending from the legL206 by way of the core legs L261 and 1.268, and the armature RA265 tothe leg 1.266. Accordingly, the armature RA265 is attracted to the fieldstructure of the :est relay R265, thereby to operate the test re- Thesubscriber at the substation A then dials the'iirst digit of thedirectory number of the called subscriber substation B at the dialmechat the substation A, thereby to transmit a nrst series of impulsesby way of the subscriber loop circuit to the line relay R260 in theselector switch 200. The relay R260 follows the dialed impulses in theusual manner. restoring each time the loop circuit is interrupted andoperating each time the loop circuit is completed. Each time the linerelay R260 restores,-

it interrupts', at RA26| and RC262, the previously traced circuit forenergizing the hold relay R210, and completes, at RA26| and RC2, thepreviously mentioned circuit for energizing in multiple the lowerwinding of the transfer-'relay R200 and the winding of the verticalmagnet M230. The last-mentioned ground, at RA2II, by way of RA2|0,RA20|, RC203 andRA210 to RC216, one branch of this circuit extendingfrom RC2" by way of the lower winding of R230 to battery, and the otherbranch of this circuit extending from RC215 by way of the winding ofM236 to battery. The hold relayR210 and the transfer relay R200 are oithe slow-to-release type. Thus, these relays remain operated duringimpulsing. Each time the vertical magnet M230 is energized, the`carriage of the Strowger mechanism 20| of the selector switch 200 isdriven one step in the vertical direction.

When the carriage of the Strowger mechanism 20| is moved away from itsnormal position one step inthe vertical direction, the sets of switch-springs S211, S218, and S239 are actuated. More particularly, the setof switch springs S211 is actuated into disengagement, thereby tointerrupt the previously traced circuit for energizing the upper windingof the transfer relay R290; the set of switch springs S216 is actuatedinto engagement, thereby to prepare a circuit. traced hereinafter, forenergizing the winding of the rotary magnet M231; and the set of switchsprings S239 is actuated into engagement, thereby to prepare a circuittraced hereinafter for energizing the winding of the release magnetM230. At the conclusion of the first digit dialed, the relay R260reoperates, thereby to interrupt, at RA26| and RC263, the previouslytraced circuit for energizing in multiple the lower winding of thetransfer relay R290, and the winding of the vertical magnet M236. Whenthis circuit is interrupted, further operation of the vertical magnetM236 is positively arrested, thereby to arrest the carriage of theStrowger mechanism 20| circuit extends from of the selector switch 200in a vertical position magnet'M231 to re: rotary magnet M231 thereby vtocause the rotary store. Upon restoring, the recompletes, at MA231, thepreviously traced circuit for energizing the winding thereof.

l The rotary magnet M231 continues to operate buzzer fashion, thereby todrive the carriage of the Strowger mechanism 20| step by step in therotary direction until the wiper set thereof engages a contact set inthe contact bank terminating a trunk line extending to an idle connectorswitch in the group of connector switches including the connector switch2I5. Assuming that the connector switch 2I5 is the li'lrst idleconnector switch in this group of connector switches, further operationof the rotary magnet M231 is arrested when the wiper 204 of the wiperset of the Strowger mechanism 20| engages the contact in the contact setterminating the control conductor C2I4 of the trunk line 2II extendingto the connector switch 2I5, the connector switch 2 I5 being marked asidle by the presence of battery potential upon the control conductorC2I4 of the trunk line 2| I. This application ,of battery potential tothe control conductor C2I4 of the trunk line 2| I completes thepreviously mentioned circuit for energizing the winding on the core legL268 of the eld structure of the test relay R265, this circuit extendingfrom ground, at RA213, by way of RA213, the winding on the core legL268, the wiper 204 and associated contact, and the control conductor C2I4 ofI the trunk line 2II to battery in the connector switchr 2I5. Whenenergized over the above-traced circuit, the winding on the core legL268 of the eld structure of the test relay R265 causes the test relayR265 to operate, as previously explained. Upon operating, the test relayR265 interrupts, at RA266 and RC261, a point in the previously tracedcircuit for energizing the rotary magnet M231, and completes, at RA266and RC268, a circuit for energizing the switching relay R2 I0, thiscircuit extending from ground, at RA212, by way of RA212, RA266', RC268,and the winding of R2I0 to battery. When energized over the above-tracedcircuit, the switching relay R2I0 operates to complete, at RA2I9, aholding circuit for energizing the windingthereof, .this circuitextending from the grounded control conductor CI I8 of the trunk lineII5 by way of RA2I9eand the winding of R2I0 to battery. Also, uponoperating, the switching relay R2I0 interrupts, at RA2I8, a furtherpoint in the previously traced circuit for energizing the winding of therotary magnet M231, and connects the trunk line II5 to the wiper set ofthe Strowger mechanism 206,

' thereby to complete a loop circuit between the subscriber substation Aand the connector switch 2 I5. At this time, the line conductor CI I6 ofthe trunk line H5 is conneced by/way of RAMI, RC2I2, and the wiper 20|and associated contact to the line conductor C2I2 of the trunk line 2|I; the line conductor CI I1 of the trunk line Ii5 is connected by way ofRA2I6, RC2I5, and the wiper 203 and associated contact tothe lineconductor C2I3 of the trunk line 2| I; and the control conductor CI I8of the trunk line H5 is connected by way of RA2I1 and the wiper 200 andassociated contact to the control conductor C2i@ of the trunk line 2H.Thus, ground potential appearing upon the control conductor CHS of thetrunk line H5 is extended by Way. of the control conductor C2I4 of thetrunk line 2H to the connector switch 2I5, thereby to cause theconnector switch to operate and complete a loop circuit between the lineconductor C2I2 and C2 I3 of the trunk line 2II and extending tothesubscriber substation A. -Also, the connector switch 2I5 operates tocause ground potentialtherein' to be applied to the control conductorC2I4 of the trunk line 2| I, thereby to retain the nder switch |30 andthe selector switch 200 of the link 60 in their operated positions.

Also, upon operating, the switching relay R2I0 interrupts, at RA2I0, a.point in the previously traced circuit for energizing the hold relayR210, and interrupts, at RA2II and RC2I3, and at RA2I4 and RC2I6,.points in the previously traced circuit for energizing in series theupper and lower windings of the line relay R260. The line relay R260immediately -restores and, shortly 1thereafter, the hold relay R210restores. Upon restoring, the hold relay R210 interrupts, at RA212, thepreviously traced circuit for energizing the winding on the core legL261 of the field structure of the test relay R265, and interrupts, atRA213, the previously traced circuit for energizing the winding on thecore leg L268 of the field structure of the test relay R265, thereby tocause the test relay R265 to restore. At this. time, the switching relayR2I0 in the selector switch 200 remains inits operated position due tothe completed holding circuit for energizing the winding thereofincluding the control conductor C2I4 of the trunk line 2II. Also, atthis time, the connector switch 2I5 is conditioned to be responsive toimpulses transmitted thereto .by way of the Iloop `circuit extendingthereto from the calling subscriber substation A.

It is noted that, when the connector switch 2I5 is busy, groundpotential appears upon the control'conductor C2 I4 of the trunk line 2|I extending thereto, this ground potential being derived at RC222 of thebattery reversing relay R220 therein and extending from RC222 by Way ofRC222, RA223 and other elements, not shown, to

the -control conductor C2I4. Also, during the course of operation of theconnector switch 2I5, booster battery potential appears upon the controlconductor C2 I4 of the trunk line 2| I extending thereto, this boosterbattery potential being derived at the battery 223 in the connectorswitch 2I5 and extending therefrom by way of RA22 I RA223 and otherelements, not shown, to the control conductor C2 I4.

It is noted that the selector switch 200 is so connected and arrangedthat it will not operate to seize the trunk line 2II when either groundpotential or booster battery potential appears upon the controlconductor C2I4. When the wiper 204 of the wiper set of the Strowgermechanism 20| engages the contact in the contact set terminating thecontrol conductor C2I4 of the trunk line 2| I, a path is completed forshortcircuiting the winding on the core leg L260 of the eld structure ofthe test relay R265 when ground potential appears upon the controlconductor C2I4 of the trunk line 2| I, this circuit extending fromground, at RA213, by way of RA213, the winding on the core leg L268, andthe wiper 200 and associated contact to the grounded control conductorC2I4 of the trunk line 2H. When the wiper 204 of the wiper set of theStrowger mechanism 20| engages the contact in the contact setterminating the control conductor C2i4 of the trunk line 2| I, a path iscompleted for venergizing the winding on the core leg L268 of the eldstructure of the test relay R265 when booster battery potential appearsupon the conthe core leg L200 o! the ileld structure of the test relayR255 is energized in the present instance, the magnetic ilux produced inthe shunt leg L260 of the field structure of the test relay R205 isaccumulative with the magnetic flux produced therein by the winding onthe core leg L26`| thereof. Accordingly, the test relay R235 is notoperated at this time, as previously noted.

Continuing now with the operation of the connector switch 2|5 to seizethe called subscriber line 230 extending to the subscriberl substationB, the subscriber at the calling subscriber substation A then dials twoadditional ldigits into the connector switch 2|5, thereby to cause theconnector switch 2|5 to operate, in the usual manner, and seize thecalled subscriber line 230. In the event the called subscriber line 230is busy, ground potential appears upon the control conductor C234thereof, thereby to cause the connector switch 2|5 to operate and returnbusy tone current over the loop circuit extending to the callingsubscriber substation A, in the usual manner. On the other hand, in theevent the called subscriber line 230 is idle, battery potential appearsupon the control conductor C234 thereof, this battery potential beingderived at` the upper terminal of the winding oi.' the cutoif relay R245of the line circuit; 240, individually associated with the subscriberline 230, and extending therefrom by way of the winding of R245, RC253and RA252 to the control conductor C234. I

'Ihe connector switch 2|5 then operates to cause direct ground potentialto be applied to the wiper 228 of the wiper set of the Strowgermechanism 225, thereby to complete a circuit for energizing the cutoffrelay R245. The circuit for energizing the cutoi relay R245 extends fromground potential appearing in the connector switch 2|5 .by way of thewiper 228 and associated contact of the Strowger mechanism 225, thecontrol conductor C234 of the subscriber line 230, RA252, RC253 and thewinding of R245 to battery. When energized over the above-tracedcircuit. the cutoil' relayv R245 operates to interrupt, at RA248 and atRA249, the circuit for energizing the line relay R250, and to complete,at RA24'I, a path for applying ground potential to the control conductorC235 oi' the subscriber line 230, this path extending from groundpotential appearing upon the control conductor C234 of the subscriberline 230, by way of RA252, RC253 and RA24I to the control conductorC235. 'I'his application of ground potential to the control conductorC235 marks the called subscriber line 230 as busy to the nder switchesof the links having access thereto. Also, upon operating, the cutoffrelay R245 completes, at RA245, a circuit for energizing the winding ofthe meter relay RZIS, assuming that the upper terminal of the meterrelay R2|9 is connected to the conductor C2|8, this circuit extendingfrom the grounded control conductor C234 of the subscriber line 230, byway oi' RA252, RC253, RANG, the conductor C2| 8, and the winding of R2I9to battery. Although the winding of the meter relay R2|9 is energizedover the above-traced circuit, this relay does not operate at; this timedue to theL fact that it is oi' the marginal type.

After seizing the called subscriber line 230, the connector switch 2|5operates to cause ringing current to be projected over the lineconductors C23| and C232 of the subscriber line 230 in the usual manner,thereby to cause the ringer at the called substationB to operate. Whenthe subscriber at the substation B answers the call by removing thetelephone receiver of the telephone instrument thereat from its hook,a'loop circuit is completed by way ot the line conductors of thesubscriber line 230 to the connector switch 2|5, thereby to cause thebattery reversing relay R220 in the connector switch 2I5 to operate inthe usual manner. Also, the connector switch 2| 5 operates to complete aconnection between the calling subscriber loop circuit extendingtheretov from the subscriber substation A and the called subscriber loopcircuit extending thereto from the substation B. Upon operating, thebattery reversing relay R220 in the connector switch 2|5 completes, atRA22I and RA223, the previously traced path for connecting boosterbattery potential to the control conductor C2|4 of the trunk line 2| I,and interrupts at RA223 and the previously traced path for connectingground potential to the control conductor C2|4 of the trunk line 2| I.'I'his application of booster battery potential to the control conductorC2|4 of the trunk line 2I| completes a circuit for effectivelyenergizing the winding of the meter relay R |00 associated with the linecircuit |00 individually associated with the calling subscriber line|0I, this circuit extending from booster battery potential appearingupon the control conductor C2|4 o1 the trunk line 2|| by way oi thewiper 204 and associated contact of the Strowger mechanism 20| of theselector switch 200, RAZII, CI I8, RA| 63, CI34,v the wiper |43 andassociated contact of the Strowger mechanism |40 of the inder switch|30, the control conductor C|04 of the subscriber line |0I, RAI I3,RAII4, C|08, and the winding of R|00 to-battery. When energized over theabove-traced circuit, the meter relay R|09 operates, thereby to cause acall register associated therewith to be actuated in the usual manner.It is noted that booster battery potential appearing uponthe controlconductor CI I8 oi.'- the trunk line ||5 extending between the iinderswitch |30 and the selector switch 200 of the link 80, and upon thecontrol conductor C|04 of the subscriber line |00, retains theseswitches and the line circuit |00 in their operated positions. Shortlyafter the connector switch 2|5 operates to cause booster batterypotential to be applied to the control conductor C2|4 of the trunk line2| I, it again operates to cause booster battery potential to be removedfrom the control conductor C2| 4 and ground potential to be reappliedthereto, thereby to retain the link 50 and the line circuit |00 in theiroperated positions.

The release of the established connectionl between the subscribersubstations A and B is under the control of the subscribers thereat and,when both of the subscribers replace the receivers of the telephoneinstruments upon their associated switchhooks at the substations A andB, the connector switch 2 I5 iirst releases. When the connector switch 2I5 is released, the Strowger mechanism 225 thereof is returned to itsnormal position and ground potential is removed in the connector switch2|5 from the control conductor C2| 4 of the trunk line 2| I. When theStrowger mechanism 225 of the connector switch 2|5 is returned to itsnormal position, the previously traced circuit for energizing the cutoirelay R245 in the line circuit 240 is interrupted, thereby to cause thecutoff relay R245 to restore. Upon restoring, the cutoir relay R245interrupts, at RA248, a point in the previously traced circuit forenergizing the meter relay R2Il, intertrunk rupts, at RA241, a point inthe previously tracedv path for applying ground potential to the controlconductor C235 of the subscriber line 230, and prepares, at RA248 and atRA248, points in the previously mentioned circuit for energizing theline relay R250. At this time, the line circuit 240 individuallyassociated with the subscriber line 230 is completely released.

When ground potential is removed from the control conductor C2 I4 ofthel trunk line 2| I, the previously traced path for connecting groundpotential to the control conductor CII8 of the line II5 extendingbetween the ilnder switch |30 and the selector switch 200 of the link 50is interrupted. When ground potential is removed from the controlconductor CI.I 8 of the trunk line II5, the previously traced holdingcircult for energizing ,the winding of the switching relay R2I0 isinterrupted, thereby -to cause the latter relay to restore. Uponrestoring, the switching relay R2I0 interrupts, at RA2I9, a furtherpoint in the holding circuit for energizing the winding thereof,prepares, at RA2I8, a point in the previously traced circuit forenergizing the winding of the rotary magnet M231, and interrupts, atRA2II and RC2|2, at RA2I4 and RC2I5 and at RA2 I1 the connection betweenthe trunk line II5 and the wiper set of the Strowger mechanism 20|, andprepares, at RA2I I and RC2I3, and at RA2I4 and RC2I6, points in thepreviously traced circuit for energizing in series the upper and lowerwindings of the line relay R260. Also, upon restoring, the switchingrelay R2I0 completes, at RA2I0, the previously mentioned circuit forenergizing the release magnet M238. this circuit extending from ground,at RA2I0, by way of RA2I0, RA26I, RC263, RA214, RC216, RA292, the set'of switch springs S239, and the winding of M238 to battery. Whenenergized over the above-traced circuit, the release magnet M238operates, thereby to release the carriage of the Strowger mechanism'20lin order.

to cause it to be returned to its normal position. When the carriage ofthe Strowger mechanism 20| is returned to its normal position, the setsof switch springs S239, S211 and S218 are actuated. More particularly,the set of switch springs S239 is actuated into disengagement, therebyto interrupt the previously traced circuit for energizing the winding ofthe release magnet M238; the set of switch springs S211 is actuated intoengagement, thereby to prepare a point in the previously traced circuitfor energizing the upper Winding of the transfer relay R290; and the setof switch springs S218 is actuated into disengagement, thereby tointerrupt a further point in the previously traced circuit forenergizing the winding of the rotary magnet M231. At this time,completely released.`

When ground potential is removed from the control conductor CII8, thepreviously traced circuit for energizing the switching relay, RI60 inthe finder switch |30 is interrupted, thereby to cause the latter relayto restore. Upon restoring, the switching relay RI60 prepares, at RAI55,a point in the previously traced circuit for energizing the winding ofthe rotary magnet MI1I, Y

interrupts, at RAI69, a point in the previously traced path for applyingground potential to the guard conductor C322, interrupts, at RAI64, afurther point in the holding circuit for energizing the winding thereof,prepares, at RAI60, a point in the previously traced circuit forenergizing the' winding of the switching relay RI50,

the selector switch 200 is and interrupts, at Ram, at nam and at asm,

the connection between the trunk line II5 andthe trunk line I3I. Also,upon restoring, the switching relay RISO interrupts. at-RAI88 and RC|81,the previously traced circuit for illumihating the supervisory lampLI28, and completes, at RAISB and RCI68, the previously mentionedcircuit for energizing the winding of the release magnet. MI12. Thelast-mentioned circuit extends from groun`d, at RAI44,'by way of RAI44,RCI45, the switch springs |88 and |81 of the busy switch SI83, theswitch springs |18 and |18 of the set of switch springs SI15,RAI68,'RCI88, RAI58, andthe winding of MI12 to battery. When energizedover the ,above-traced circuit, the release magnet release thecarriageof the Strowger Amechanism |40 and to cause it to be returned toits normal position. When the carriage of ythe Strowger mechanism .isreturned to its normal' position, the sets of switch springs SI15 andSI19 are actuated. More particularly, the switch springs |80 and I8Iofthe set of switch springs SI19 are actuated into disengagement,thereby to interrupt a further point in the previously traced path forapplying ground potential to the guard conductor C322; the switchsprings I8I and |82 are actuated intol engagement, thereby to connectthe guard conductor C322 to the control conductor CI I8 of the trunkline I'I5; the switch springs |16 and |18 of the set of switchv springsSI15 are actuated into disengagement, thereby to interrupt thepreviously traced circuit for energizing the winding of the releasemagnet MI12; and the switch springs |11 and |18 of the set of switchsprings SI15 are actuated into engagement, thereby to complete thepreviously traced path for applying groundA potential in thev finderswitch |30 to the all-trunks-,busy conductor C 32I. The previouslymentioned connection between the guard conductor C322 and the controlconductor CII8 of the from the guard conductor C322, by way of theswitch springs |84 and |85 of the busy switch SI83, RAI43, and theswitch springs I8I and |82 of the set of switch springs ySI19 to thecontrol conductor CI I8 of the' trunk line |I5. The connection of theguard conductor C322 to the control conductor CI I8 of the trunk lineII5 insures that the link 60 will not be selected by the distributor 300for the use of a calling one of the lines unless both the iinder switch|30 and the connector switch 200 thereof are completely released. Atthis time,- the nder switch |30 is completely released. Accordingly, thelink 60 is completelyrelease and is available to beselected by thedistributor 300 for the use of a calling one of the lines. r

When ground potential is removed from the control conductor CI I8 of thetrunk line I|5, the previously traced circuit for energizing the cutoffrelay RI I0 in the line circuit |00 individually associated with thesubscriber line IOI is inrelay RI09-associated with the line circuitI00.,

At this time, th'e `line circuit |00 is completely releasedand thesubscriber line IOI is marked as MI12 operates, thereby, tol

trunk line II5 extends

